Thermal transport in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6+\mathrm{x}}$: Doping dependence across the phase diagram

A systematic study of the temperature and oxygen-doping dependence of thermal conductivity (κ) and thermoelectric power (S) in polycrystal ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{6+\mathrm{x}}$ is reported for compositions spanning the phase diagram (0<x<1). κ(x) is nonmonotonic with apparent enhancements near x=0.1, 0.3, and 0.6. Thermal hysteresis in κ and S with a common temperature dependence is observed for all x, and is substantially enhanced at these same compositions. These features are likely related to the oxygen order and associated changes in the local structure. The superconducting-state enhancement of κ is parametrized by its change in slope at the superconducting transition. The doping dependence of this quantity agrees with that of the in-plane thermal conductivity in single crystals, and confirms that the enhancement scales with the superconducting condensate density throughout the underdoped regime.